* {
    margin: 0;
    padding: 0;
}
.box {
    /* 
        vw:视图窗口宽度的计算值 100vw === 视图窗口宽度100%
        vh:视图窗口高度的计算值 100vh === 视图窗口高度100%
    */
    height: 100vh;
    background-color: black;
}
.box>img {
    position: absolute;
    z-index: 10;
    /* calc() 计算  */
    /* 图片大小：50*62 */
    left: calc(50% - 25px);
    top: calc(100% - 62px);
}
.zidan{
    position: absolute;
    top: calc(100% - 62px);
    left: calc(50% - 25px);
    width: 10px;
    height: 40px;
    border-top: 1px solid #ffffff;
    background-image: linear-gradient(rgb(255, 47, 0),rgb(255, 255, 255),rgb(45, 124, 244),rgba(13, 0, 255, 0.59));
    border-top-left-radius: 100%;
    border-top-right-radius: 100%;
    transition: top 0s linear;
    
}